I am looking at purchasing a large-ish CNC mill, but these generally require
220VAC 3-phase, though some require 220VAC 1-phase. At the same time, I'm
also looking into renting an apartment, but finding an attached garage (so I
can get 220V from the panel or dryer outlet in the garage) seems to be iffy.
Detached garages only have 110V, and I'm not sure if this will be a
show-stopper. This is in the USA, btw.

First, 220V 3-phase is not a problem to get from 220V 1-phase, using a phase
converter. But 220V 1-phase seems to be a problem...

If I get 220V from a dryer outlet, I understand that there are grounding
differences (dryer outlets are grounded to neutral?) that could be a
show-stopper in using the mill, which expect to be grounded to earth. Is
there a fix for this?

If I get 220V from a breaker panel, is it the same as the dryer outlet? Or
would I be able to get properly-grounded 220V there?

If I use the 110V outlet, I can step that up using a transformer, but I'm
limited to 15A. That would be ~7A or less at 220V, factoring in transformer
inefficiency. And the mill's spindle motor needs more than that. However,
I'm wondering why the power outlet is limited to 15A? Is it because of the
wiring? If there are multiple outlets in the garage, and each is rated to
15A, then I should be able to find the "first" outlet in the garage (where
the supply wires come into the garage) and wire up a beefier outlet at that
point. The wiring up to that point should be able to handle more current --
theoretically 15A x Num_Outlets. Is this correct? I'd also need to change
the breaker for this circuit.

I don't mind getting an electrician in there to add an outlet and run some
lines from the breaker panel, etc, but I can't get them to run larger lines
into the garage without raising some eyebrows.

15A is limited by the size of the wire (#14) in the wall. Your outlets are
all parallel after that. 15A is all you get for *all* outlets. If you put
a larger breaker in the mains w/out changing out the wiring you will get a
visit from the fire department.

The dryer outlet is your best bet. 240 is essentially 2@120 lines 180
degrees out of phase, so it's not really tied to neutral the same way 120
is, but it is still tied on that third pin. Neutral is ground for all
intents and purposes, which kind of makes it 2-phase with respect to the
neutral line. I'm a little hazy on that one.

Some of the tools in my shop run on 220 and they are wired no differently
than the dryer is.

> If I get 220V from a dryer outlet, I understand that there are grounding
> differences (dryer outlets are grounded to neutral?) that could be a
> show-stopper in using the mill, which expect to be grounded to earth. Is
> there a fix for this?
older drier outlets use a combined ground and neutral making them slightly
less safe, newer ones have them seperate, either way that shouldn't affect
your appliances operation.

> The wiring up to that point should be able to handle more
> current --
> theoretically 15A x Num_Outlets. Is this correct? I'd also need
> to change
> the breaker for this circuit.
unlikely, the whole circuit is only likely to be rated at 15 or 20 amps
total

> I don't mind getting an electrician in there to add an outlet and
> run some
> lines from the breaker panel, etc, but I can't get them to run
> larger lines
> into the garage without raising some eyebrows.
is there something illegal about having a CNC mill in your garage? why can't
you tell the electrician what you wan't power for?

> -----Original Message-----
> From: spam_OUTpiclist-bouncesTakeThisOuTmit.edu [.....piclist-bouncesKILLspam@spam@mit.edu]On Behalf
> Of PicDude
> Sent: Tuesday, October 17, 2006 4:03 PM
>
> wiring? If there are multiple outlets in the garage, and each is
> rated to
> 15A, then I should be able to find the "first" outlet in the
> garage (where
> the supply wires come into the garage) and wire up a beefier
> outlet at that
> point. The wiring up to that point should be able to handle more
> current --
> theoretically 15A x Num_Outlets. Is this correct?

Heavens No. For example, if there were 6 outlets in the garage there is no
way the wiring is going to handle 90A.

> I'd also need
> to change
> the breaker for this circuit.

Don't do it. You're going to need either an Electrician or a Fireman. I'd go
with the Electrician.

> Hi all,
>
> I am looking at purchasing a large-ish CNC mill, but these generally require
> 220VAC 3-phase, though some require 220VAC 1-phase. At the same time, I'm
> also looking into renting an apartment, but finding an attached garage (so I
> can get 220V from the panel or dryer outlet in the garage) seems to be iffy.
> Detached garages only have 110V, and I'm not sure if this will be a
> show-stopper. This is in the USA, btw.
>
> First, 220V 3-phase is not a problem to get from 220V 1-phase, using a phase
> converter. But 220V 1-phase seems to be a problem...
>
> If I get 220V from a dryer outlet, I understand that there are grounding
> differences (dryer outlets are grounded to neutral?) that could be a
> show-stopper in using the mill, which expect to be grounded to earth. Is
> there a fix for this?
>
> If I get 220V from a breaker panel, is it the same as the dryer outlet? Or
> would I be able to get properly-grounded 220V there?
>
> If I use the 110V outlet, I can step that up using a transformer, but I'm
> limited to 15A. That would be ~7A or less at 220V, factoring in transformer
> inefficiency. And the mill's spindle motor needs more than that. However,
> I'm wondering why the power outlet is limited to 15A? Is it because of the
> wiring? If there are multiple outlets in the garage, and each is rated to
> 15A, then I should be able to find the "first" outlet in the garage (where
> the supply wires come into the garage) and wire up a beefier outlet at that
> point. The wiring up to that point should be able to handle more current --
> theoretically 15A x Num_Outlets. Is this correct? I'd also need to change
> the breaker for this circuit.
>
> I don't mind getting an electrician in there to add an outlet and run some
> lines from the breaker panel, etc, but I can't get them to run larger lines
> into the garage without raising some eyebrows.
>
> Cheers,
> -Neil.

In the US house wiring is typically brought in from the pole as
center tapped 220V.The center tap is connected to earth ground and 110is
derived from one side of the secondary winding and the center tap. The 220 is
derived from the entire secondary winding and is only 220 across the
winding not to ground.Where dryer outlets are grounded depends on the
local wiring code, it could be either neutral,earth ground or both .The
15A restriction could be because of wiring,outlet capacity or both.You
might check the local library for a copy of the NEC handbook.It can
answer many of your questions with specific examples and many towns base their
wiring codes on it.
Ray Warren

> Don't do it. You're going to need either an Electrician or a Fireman. I'd go
> with the Electrician.
>

In order to prevent visit from a Fireman, I would also recommend to check what
the Electrician did. I had to replace my electric stove this weekend, because
the Electrician has failed to tighten the nuts on 220V wiring on the old
stove. I am very surprised I did not have fire, because one wire has burned
completely off of its terminal! The other wire was just touching the terminal,
its nut was just put on the thread and not tightened at all!

On Tuesday 17 October 2006 4:02 pm, PicDude wrote:
> Hi all,
>
> I am looking at purchasing a large-ish CNC mill, but these generally
> require 220VAC 3-phase, though some require 220VAC 1-phase. At the same
> time, I'm also looking into renting an apartment, but finding an attached
> garage (so I can get 220V from the panel or dryer outlet in the garage)
> seems to be iffy. Detached garages only have 110V, and I'm not sure if this
> will be a show-stopper. This is in the USA, btw.
>
> First, 220V 3-phase is not a problem to get from 220V 1-phase, using a
> phase converter. But 220V 1-phase seems to be a problem...

>
> If I get 220V from a dryer outlet, I understand that there are grounding
> differences (dryer outlets are grounded to neutral?) that could be a
> show-stopper in using the mill, which expect to be grounded to earth. Is
> there a fix for this?

First off NEC allows two different configurations. 3 wire and 4 wire. so
3 wire is L1, L2, Ground
4 wire is L1,L2,Ground, Neutral.

you can get 220 accross L1, L2 without using either ground or neutral.
ground is for safety.
neutral is for splitting phases into 110v..

This change was put into NEC because some stoves/dryers have 110v components.
and they were using ground to power them..

Grounds and neutrals are ONLY allowed to be tied together at the source.. ie
the supply panel..

>
> If I get 220V from a breaker panel, is it the same as the dryer outlet? Or
> would I be able to get properly-grounded 220V there?

>
> If I use the 110V outlet, I can step that up using a transformer, but I'm
> limited to 15A. That would be ~7A or less at 220V, factoring in
> transformer inefficiency. And the mill's spindle motor needs more than
> that. However, I'm wondering why the power outlet is limited to 15A? Is
> it because of the wiring? If there are multiple outlets in the garage, and
> each is rated to 15A, then I should be able to find the "first" outlet in
> the garage (where the supply wires come into the garage) and wire up a
> beefier outlet at that point. The wiring up to that point should be able
> to handle more current -- theoretically 15A x Num_Outlets. Is this
> correct? I'd also need to change the breaker for this circuit.

No this is not correct.. the breaker is sized in order to trip on the lowest
common demonator.. ie wiring size, plug capacity etc.. So the most you can
get from a 15A branch is 15A doesn't matter if you have 1000 plugs on the
branch.

I think the easiest answer to the problem is to change the CNC's motor to a
proper single phase 220 volt.. Fred
>
> I don't mind getting an electrician in there to add an outlet and run some
> lines from the breaker panel, etc, but I can't get them to run larger lines
> into the garage without raising some eyebrows.
>
> Cheers,
> -Neil.

> This change was put into NEC because some stoves/dryers have 110v
> components.
> and they were using ground to power them..
i'm pretty sure that the connection on the nema 10 series is technically
considered a neutral despite the fact it was used as a ground as well in
older drier installation.

> In the US house wiring is typically brought in from the pole as
> center tapped 220V.

I've always wondered about this... It seems that in the US, the electricity
companies have two different types of consumer nets: the two-phase
residential net, and a three-phase net in industrial areas.

What about mixed areas, with both machine shops and residences in the same
street? Do they lay both nets, or do the residences get three phases, or do
the shops get two phases only?

They run three phase most places, for residential they take one of the phases and run it through a center tapped transformer to create split phase. Since the transformer is isolated, they ground the center tap and the residence sees "normal" two phase. There is some effort made to load ballance the three phases by putting different customers on each phase.

>> In the US house wiring is typically brought in from the pole as
>> center tapped 220V.
>
> I've always wondered about this... It seems that in the US, the electricity
> companies have two different types of consumer nets: the two-phase
> residential net, and a three-phase net in industrial areas.
>
> What about mixed areas, with both machine shops and residences in the same
> street? Do they lay both nets, or do the residences get three phases, or do
> the shops get two phases only?

Power generated in three-phase, distributed in 3-phase, eventually a
pair of phases is selected for residential distribution and run into a
neighborhood/street. Some properties are closer to the 3-phase lines
than others.

Over time, if the 2-phase split loads are not kept well balanced, the
3-phase customers on that segment start to notice.

It is my impression that if a customer wants 3-phase, they are "allowed"
to pay the utility the costs of placing the poles/lines. Thus, it is
nice to locate where 3-phase is already laid. I know a wood-working
shop that decided it was cheaper to install and run a large 3-phase
generator than to buy the several miles of 3-phase connection.

Gerhard Fiedler wrote:
> Ray Warren wrote:
>
>
>> In the US house wiring is typically brought in from the pole as
>> center tapped 220V.
>>
>
> I've always wondered about this... It seems that in the US, the electricity
> companies have two different types of consumer nets: the two-phase
> residential net, and a three-phase net in industrial areas.
>
> What about mixed areas, with both machine shops and residences in the same
> street? Do they lay both nets, or do the residences get three phases, or do
> the shops get two phases only?
>
> Gerhard
>
>

My understanding is that (in Canada) they distribute 3phase at high
voltage. They then, for residences, tap different phases at different
transformers, such, that in aggregate, the various transformers load
each phase approximately equally. Industrial customers get a supply
transformed from all three phases. Of course, I may be completely wrong.

The problem with Edison's DC power system was that you need very large
wire to carry DC any distance and keep losses down. With Tesla's system
AC it can be transformed up and down in voltage. It seems that there's
some relation between the voltage and the distance. Long cross country
lines may be over 100 kV. On the same pole in a California city there
may be 12 kV (3 phase = 3 wires) at the top of the pole, 3 kV (might be
2 wires = single phase or 3 phase) lower down and 220 V (single phase)
that feeds maybe 4 houses. The 220 V comes from a center tapped
transformer. The purpose of the center tap is to that if there's a
primary to secondary short in the transformer you don't get 3 kV coming
into your house. This is also why you need an earth ground at the entry
panel.

If the neutral wire coming into your house opens then the voltages at
the 110 V sockets will depend on how the loads in your house balance.
If instead of being opened there's excessive resistance in the neutral
and the loads are not well balanced then the voltage at the outlets on
one side will be low and on the other high. This can cause light bulbs
to burn out early, etc.

> Power generated in three-phase, distributed in 3-phase, eventually a
> pair of phases is selected for residential distribution and run into a
> neighborhood/street.

The pair of phases that normal people have in normal homes are definitely
not two phases of a three-phase system, if that is what you meant. The
phases in a three-phase system are 120° apart; the two phases in normal US
homes are 180° apart. The voltage between two phases of a three-phase
system is not double the voltage of one phase to ground, it's sqrt(3).

I'm speaking with experience of wiring in the UK, which isn't all that
much different...

Here, 3 phases are not wired to domestic customers because they don't
need 3 phases. Most single phase supplies are fused at 100A, which is
more than enough for a regular house. Wiring 3 phases costs a bunch
more, and takes much of the phase balancing control outside the
control of the network operator.

Furthermore, running 3 phases to a residence can make the installation
less safe. Since only motors actually use 3 phases, other equipment
(lighting, sockets) is tied to one of the three phases.

So, the installer has to decide how to make that split - and if he
chooses unwisely then in a fault scenario the unlucky homeowner could
be subject to a fault PD of 415V (we have 230V here in the UK, so
P1-P2 Vrms is 415V), which is more dangerous than the regular 230V.

Also, wiring certain lighting systems to different phases (basically,
virtually any non incandescent lighting) can cause a perceptible
flicker, if the installation allows a user to see lighting running
from different phases at the same time.

OOI, is 15A a typical breaker rating for a socket circuit in the US?
15A * 110V = only 1650W - it must take ages to boil a kettle etc etc.

>
> Denny Esterline wrote:
>
> > They run three phase most places, for residential they take one of the
> > phases and run it through a center tapped transformer to create split
> > phase.
>
> But it's probably still the case then that in residential areas the
> existing wiring is the two-phase wiring, and only if you're exceptionally
> lucky you have a three-phase wiring nearby -- right?
>
> Is there a technical reason not to wire three phases to residences?
>
> Gerhard

Does cost count as a "technical" reason? I'm sure there's room to argue but
in general I would say that three phase is more expensive to run then split
phase. And considering most residential applications are not large motors,
three phase looses it's primary benefit.

> They run three phase most places, for residential they take one of the phases and run it through a center
> tapped transformer to create split phase.
> Since the transformer is isolated, they ground the center tap and the residence sees "normal" two phase.
> There is some effort made to load ballance the three phases by putting different customers on each phase.

Ah, that explains it! I was going to ask how they can connect people to different pairs of phases and ground the centre of each one without current
flowing between the different phase-pairs' ground connections - the isolating transformer answers that one! Do they tend to have three
transformers together, and feed houses in the same street, or do they have one phase per street?

Over here everything is three-phase: generation, transmission and distribution, until it gets to the individual property. At the local end of things there
is a "substation" which has a 3-phase Wye-wound transformer that brings it down from 11kV to (nominally) 400V 3-phase, and a 3-phase cable runs
from here down the street and each house in turn is fed one phase which gives a nominal 230V (I have a blue label with "B" on my distrubution board,
so I'm on the Blue phase). Neutral is taken from the centre of the Wye-transformer, and it's earthed at the transformer, and fed to each house.
Earthing varies - it may be fed from the transformer using the cable sheath, or by bonding to Neutral at the service head, or (especially when the
feed is overhead) from having a spike at the house. The upshot is that there is only one form of power in a house, 230V between Live & Neutral, and
(mostly) only one plug & socket design, usually known as "13 Amp", into which you can plug just about anything, giving about 3kW at each socket.

If you're doing something industrial that needs more than 3kW you can either hard-wire, or use industrial plugs which handle 16 or 32A, but you'd
never normally see those in a house or garage, even a garage-workshop.

On 10/18/06, slippyr4 <.....slippyr4KILLspam.....gmail.com> wrote:
> OOI, is 15A a typical breaker rating for a socket circuit in the US?
> 15A * 110V = only 1650W - it must take ages to boil a kettle etc etc.

Stoves, Dryers, Water heaters, air conditioners, etc are often run
from 240VAC, 30A or higher circuits.

But even a 120V 15A microwave can boil water on 1000W, so it's not
always how much wattage you have, it's how you use it... :-)

>> Power generated in three-phase, distributed in 3-phase, eventually a
>> pair of phases is selected for residential distribution and run into a
>> neighborhood/street.
>
> The pair of phases that normal people have in normal homes are definitely
> not two phases of a three-phase system, if that is what you meant. The
> phases in a three-phase system are 120° apart; the two phases in normal US
> homes are 180° apart. The voltage between two phases of a three-phase
> system is not double the voltage of one phase to ground, it's sqrt(3).

You are indisputably correct; I said that wrong. Others have stated the
correct details.

That's debatable. Of course, in the end, we don't even need electricity...
:) But the start of the thread was a domestic customer who wants to buy a
professional power tool (these types exist :) and has to go to lengths
because he doesn't have 3 phases in the home. He probably disagrees with
you.

In a country where a normal house does not have 3 phase wiring, there won't
be many 3 phase devices for sale for use in residences. Which of course may
reasonably be quite different in a place where houses usually do have 3
phases wired. So in a way, the infrastructure availability drives the
perceived need -- and the perceived need doesn't say that much about the
relative merits.

> Wiring 3 phases costs a bunch more,

Maybe. But I think one would have to take the whole infrastructure cost
into account. I don't know really what all the equipment costs and how it
is installed in the different scenarios. I'm not sure there are comparisons
easily available (even though they probably exist), and such a cost
comparison is probably not trivial.

For example, it seems that in the USA there must be many areas where both a
3 phase net is wired (along the streets) and the normal residence net.

> and takes much of the phase balancing control outside the control of the
> network operator.

This I don't buy. In the end, it's statistics, and it doesn't really matter
that much whether you give the individual homes 1 or 3 phases. There
probably can be made a statistical argument that with 3 phases wired the
distribution is better, because differences between individual homes tend
to affect the phases less. Also, if everybody has 3 phase wiring, high
power equipment like central electric heaters/boilers tend to be sold in 3
phase versions, which is good for the phase balance.

> Furthermore, running 3 phases to a residence can make the installation
> less safe. Since only motors actually use 3 phases, other equipment
> (lighting, sockets) is tied to one of the three phases.
>
> So, the installer has to decide how to make that split - and if he
> chooses unwisely then in a fault scenario the unlucky homeowner could
> be subject to a fault PD of 415V (we have 230V here in the UK, so
> P1-P2 Vrms is 415V), which is more dangerous than the regular 230V.

How would that happen? Can you describe a scenario (with legal wiring :)
where a user would be connected between two phases?

> Also, wiring certain lighting systems to different phases (basically,
> virtually any non incandescent lighting) can cause a perceptible
> flicker, if the installation allows a user to see lighting running
> from different phases at the same time.

> Also, wiring certain lighting systems to different phases (basically,
> virtually any non incandescent lighting) can cause a perceptible
> flicker, if the installation allows a user to see lighting running
> from different phases at the same time.
as another poster has guessed this is backwards, we deliberately put
lighting on different phases to reduce the flicker affects.

single ended single phase:
pros:
safe (highest voltage present is the utilisation voltage)
cheap for small loads because only two wires and only one breaker mechanism.
can be derived from a single phase MV supply
cons:
expensive for high powers
causes motors and generators to be less efficiant and produce more
vibration.
causes stroboscopic effects with flourescent lighting
can't supply power at double the standard single phase voltage

split single phase
pros:
cheaper than 3 phase for small to moderate loads because only two wires and
only one breaker mechanism.
cheaper than single ended single phase for moderate to large loads
can be derived from a single phase MV supply
cons:
more expensive than 3 phase for high powers because of cable use
causes motors and generators to be less efficiant and produce more
vibration.
causes stroboscopic effects with flourescent lighting
highest voltages present of the systems here.

3 phase wye
pros:
cheapest system for high power use at the standard single phase voltage
allows for efficiant generators and motors.
allows stroboscopic effects to be reduced by splitting lighting over the
phases.
cons:
requires a three phase MV supply
can't supply power at double the standard single phase voltage

3 phase delta with ground/neutral on midpoint of one winding.
pros:
efficiant if most of the load is at twice the standard single phase voltage
(e.g. heating in the USA)
allows for efficiant generators and motors.
cons:
causes stroboscopic effects with flourescent lighting (since all the single
phase load at the standard utilisation voltage must be placed on one phase).
for the 3 phase system to be balanced two thirds of the single phase load
must be at twice the standard utilisation voltage.

> > They run three phase most places, for residential they take one of the phases and run it through a center
> > tapped transformer to create split phase.
> > Since the transformer is isolated, they ground the center tap and the residence sees "normal" two phase.
> > There is some effort made to load ballance the three phases by putting different customers on each phase.
>
> Ah, that explains it! I was going to ask how they can connect people to different pairs of phases and ground the centre of each one without current
> flowing between the different phase-pairs' ground connections - the isolating transformer answers that one! Do they tend to have three
> transformers together, and feed houses in the same street, or do they have one phase per street?

I've certainly seen both. In very rural areas (where it's not uncommon for larger farms to want/need three phase anyway) they tend to have one transformer servicing one house - maybe a couple if they're close. In more urban areas it gets a fair bit more complicated and the trend over the past few decades has been to bury the lines, thus it's much more difficult for the casual observer to discern.

> Over here everything is three-phase: generation, transmission and distribution, until it gets to the individual property. At the local end of things there
> is a "substation" which has a 3-phase Wye-wound transformer that brings it down from 11kV to (nominally) 400V 3-phase, and a 3-phase cable runs
> from here down the street and each house in turn is fed one phase which gives a nominal 230V (I have a blue label with "B" on my distrubution board,
> so I'm on the Blue phase). Neutral is taken from the centre of the Wye-transformer, and it's earthed at the transformer, and fed to each house.
> Earthing varies - it may be fed from the transformer using the cable sheath, or by bonding to Neutral at the service head, or (especially when the
> feed is overhead) from having a spike at the house. The upshot is that there is only one form of power in a house, 230V between Live & Neutral, and
> (mostly) only one plug & socket design, usually known as "13 Amp", into which you can plug just about anything, giving about 3kW at each socket.
>

I read the history of British electrical systems once and as I recall, the loop system was implemented to save metal. Since any plug is actually fed from both sides of the loop the wire only needs to be rated for ~1/2 the total current. Ours is a single ended daisy chain, so the wire must be rated for the full current. But we only have a fuse/breaker at the service panel, so the sum current of the entire string can't exceed the rated current. In practice handheld appliances seem to rated less than 1500W (hair dryers, electric fry pans, tea kettles etc)

> If you're doing something industrial that needs more than 3kW you can either hard-wire, or use industrial plugs which handle 16 or 32A, but you'd
> never normally see those in a house or garage, even a garage-workshop.
>

Most commonly circuits are 14ga wire and rated for 15 amps. Some specific circuits are rated for 20 amps and use 12ga wire (I believe it's 2 in the kitchen by local code) and usually in the utility area (garage, basement, outdoor...) But just to make things complicated they fit the same plug. (there are differences between 15 and 20 amp rated sockets, but the consumer can't tell the difference by looking) It's still safe though, because a 15 amp socket is protected by a 15 amp breaker. But it can certainly be annoying.

Hard wire is reasonably common for lots of things, but we also have a myriad of other plugs for high current devices to about 50A. Electric clothes dryers at 220V 30A, electric ranges at 220V 50A. Higher than that is common enough in industrial settings (I've seen 480V 500A three phase connectors)

Another interesting quirk is the voltage. It's common to talk about 110/220, but some people say 120/240. The plug next to me actually measures 117V. Some other places I've lived were closer to 110V and I worked in one place that measured 124V. And even though the USA is "standardized" on 60 Hz, I believe there are a couple small islands up near Maine that use 50Hz and last I knew there was a generator plant at Niagara Falls that produces 25Hz for a few industrial customers.

As they say, The best thing about standards is there are so many to choose from.

> I read the history of British electrical systems once and as I recall, the loop system was implemented to save metal. Since any plug is actually fed from both sides of the loop the wire only needs to be rated for ~1/2 the total current. Ours is a single ended daisy chain, so the wire must be rated for the full current. But we only have a fuse/breaker at the service panel, so the sum current of the entire string can't exceed the rated current. In practice handheld appliances seem to rated less than 1500W (hair dryers, electric fry pans, tea kettles etc)
>

It's true. We call it a "ring final" circuit. It's other benefit is
that the CPC (the ground) is connected from two places, so is half as
likely to be broken.

Every socket in the UK has an earth (ground) pin (at least every
socket made since the '20s). Every plug has a fuse in it, although in
some situations a faulty appliance may trip the circuit's breaker
rather than blow the fuse (due to the fuse blow characteristics)

Your handheld appliances are all rated below 1500W because of the way
your houses are wired. Over here, it's common for appliances to pull
much more - because they can. Kettles are often 2-2.5KW, we have
electric heaters at 2KW, etc. Of course, yours still work - but ours
boil the water / heat the house quicker.

> > If you're doing something industrial that needs more than 3kW you can either hard-wire, or use industrial plugs which handle 16 or 32A, but you'd
> > never normally see those in a house or garage, even a garage-workshop.
> >

That's the same here. The maximum any one socket is designed to deliver is 13A.

>
> Most commonly circuits are 14ga wire and rated for 15 amps. Some specific circuits are rated for 20 amps and use 12ga wire

We measure cable here in square millimetres. But, according the IEE
Wiring Regulations (the UK electrical code), a cable doesn't have a
rating *per se*. Rather the designer of the installation must
calculate a suitable size of cable based on it's expected load, length
(for meeting voltage drop requirements), the way it's installed (ie,
embedded in a wall, clipped to a wall) for thermal derating, and
whether it's grouped with other cables, as well as the earth fault
loop impedance (which must be low enough to ensure that the circuit
breakers will break within the required time when a dead short
occurs).

>
> Hard wire is reasonably common for lots of things, but we also have a myriad of other plugs for high current devices to about 50A. Electric clothes dryers at 220V 30A, electric ranges at 220V 50A. Higher than that is common enough in industrial settings (I've seen 480V 500A three phase connectors)

cookers and showers are the only *common* domestic hard wired appliances here.

>
> Another interesting quirk is the voltage. It's common to talk about 110/220, but some people say 120/240. The plug next to me actually measures 117V. Some other places I've lived were closer to 110V and I worked in one place that measured 124V. And even though the USA is "standardized" on 60 Hz, I believe there are a couple small islands up near Maine that use 50Hz and last I knew there was a generator plant at Niagara Falls that produces 25Hz for a few industrial customers.

Europe used to have a nominal 220V, and the UK used to have a nominal
240V. But these nominal voltages were defined with a tolerance.

Recently, the nominal voltage in europe has been changed, to 230V.
But, sneakily, the tolerances changed with it - in the UK it's 230V
+6%/-10% . I believe (but not certain) that continental europe is 230V
-6%/+10%.

However, most houses still see about 240V at the wall. The tolerances
neatly shift the burden of compatibility onto appliance manufacturers.

>
> As they say, The best thing about standards is there are so many to choose from.
>
I think that's one of the advantages of the fact that the UK is so
small - we just have one standard.

I know in NZ if an electric stove/oven is fitted, then often two phases
are wired into the house, and the stove has a jumper point on the
connection block that allows the elements to be split between phases or
joined together to run on a single phase. The idea seems to be that a
high power item such as this is best split between phases where
practical to minimise phase balance problems but if costs of providing
the second phase get prohibitive for the advantage then it can be run on
a single phase.

> Most commonly circuits are 14ga wire and rated for 15 amps. Some
> specific circuits are rated for 20 amps and use 12ga wire (I believe
> it's 2 in the kitchen by local code) and usually in the utility area
> (garage, basement, outdoor...)

NEC changed in the last 10-20(?) years to specify 2 circuits in the
kitchen, 1 in the laudry area, 1 in each bathroom, 1 in garage, and
a bunch of other residential wiring details. I'm showing my age...

> But just to make things complicated they fit the same plug. (there
> are differences between 15 and 20 amp rated sockets, but the consumer
> can't tell the difference by looking). It's still safe though, because
> a 15 amp socket is protected by a 15 amp breaker. But it can certainly
> be annoying.

It's easy to tell the difference. If a device draws 15 amps or less,
the standard plug has 1 round ground prong and 2 vertical blades for
hot & neutral. If a device will draw between 15 and 20 amps, then the
hot blade is horizontal (neutral blade is vertical & ground is round).

Normal 15 amp duplex wall outlet can be used on either a 15A or 20A
circuit and both blade jacks are vertical. Dual use duplex outlets
have a T shape hot blade so you can insert either a vertical or a
horizontal blade. "20 amp only" outlets have vertical neutral and
horizontal hot.

> but we also have a myriad of other plugs for high current devices to
> about 50A.

Once you get above 120V 20A, the number of plug styles seems to
grow exponentially. And the number of places where you can buy
the more exotic ones approaches one over infinity. :-)

> I am looking at purchasing a large-ish CNC mill, but these generally
> require 220VAC 3-phase, though some require 220VAC 1-phase. At the
> same time, I'm also looking into renting an apartment, but finding an
> attached garage (so I can get 220V from the panel or dryer outlet in
> the garage) seems to be iffy.

> First, 220V 3-phase is not a problem to get from 220V 1-phase, using
> a phase converter.

For use with a mill, most any style of phase converter will work fine.
Less expensive capacitor type phase converters aren't appropriate for
higher load applications -- but that doesn't apply here.

> But 220V 1-phase seems to be a problem...

It shouldn't be.

Note -- all my experience is with electric service in the southwest
United States (California to Texas). East coast may be "funny"; I
just don't know.

Note -- when I say 240V, I mean generic 240V. Exact voltage may be
anywhere from 220V to 240V depending on service provider, time of day
(load), etc, etc. Same with 120V; it may vary.

As others have stated, almost all residential service is provided by
utility company having a high voltage (usually 12KV) line on the pole
[logical pole, service may be underground]. It is stepped down via
transformer to 240V single phase with a center tap.

Outlets and lighting are supposed to be distributed so that half
of load is on each hot line (but obviously it varies as different
appliances are used).

You should expect pole end of the neutral line to be hooked to a
reasonable earth ground somewhere around the transformer.

Neutral line from pole is hooked up to ground distribution bus bar
inside breaker panel. House is supposed to have a good quality earth
ground with high ampacity wire connecting it to panel's ground bus.
So neutral line from pole should be grounded at both ends (i.e. on
the pole and inside the house's breaker panel).

All ground wires and neutral wires for inside house wiring are tied
to that one ground bus bar inside the panel. In othe words, all of
the grounds and neutral should be tied together at the panel.

> If I get 220V from a dryer outlet, I understand that there are
> grounding differences (dryer outlets are grounded to neutral?) that
> could be a show-stopper in using the mill, which expect to be grounded
> to earth. Is there a fix for this?

> If I get 220V from a breaker panel, is it the same as the dryer outlet?

Yes. It will be the 2 hot wires from the panel to your outlet be it
for an electric range, electric oven, or electric dryer.

> Or would I be able to get properly-grounded 220V there?

Dryer outlet may be either 3-wire (older) or 4-wire (newer).

3-wire has 2 hot wires & 1 neutral wire. Note that neutral wire is
tied to ground bus bar inside the panel. So it is the _same_ as a
ground wire. However, if you are using the neutral wire to carry
significant current (i.e. 120V table drive motor(s) or 120V lights
on your 240V mill), then its usefullness as a ground wire decreases.
Neutral wires can carry current. Ground wires should be limited to
only carry current in exceptional circumstances (i.e. safety ground).

Assuming you have a 3-wire dryer outlet in your garage, you could
simulate 4-wire service by tying the 4-wire outlet's neutral and
ground to the single neutral wire available in the dryer outlet.
And it could even be reasonably safe if your equipment doesn't put
any (or puts very little) load on the 4-wire outlet's neutral line.

Or you could add just a ground wire to the 3-wire dryer outlet and
upgrade it to true 4-wire style.

> If I use the 110V outlet, I can step that up using a transformer,
> but I'm limited to 15A.

Yes and no. The amperage available on a single circuit is based on
the size of the circuit interrupter (fuse or breaker) (per National
Electric Code or NEC). In the United States, the 2 common circuit
interrupter sizes for common residential outlet wiring are 15 amps
and 20 amps.

15 amp service generally requires use of 14 gauge (or larger) wire.
This is all based on the temperature rise in the wire caused by
current flow, wire resistance, type of insulation, and cooling air
flow (conduit versus open wiring). Open wire, cooled by free air
circulation, can handle more current. Most wire is in walls, so
14 gauge is usually restricted to 15 amps.

20 amp service generally requires use of 12 gauge (or larger) wire.

30 amp or 40 amp service for electric dryers, electric ovens, and
such requires larger gauge wire. See ampacity tables in NEC.

Note -- NEC is published by the NFPA (National Fire Protection
Association; i.e. owned by fire insurance companies) so their one
goal is standards to protect people and structures from hazardous
conditions like overheated wires that can start fires.

Notice that wire size is basically independant of voltage. It is
based on maximum current flow and wire resistance which leads to
temperature rise. Goal is to prevent overheating & fires.

A 120V circuit has 1 hot wire so it has a single pole breaker.

A 240V circuit has 2 hot wires, so it _must_ have a ganged dual
pole breaker. If current flow in either hot wire is interrupted,
the current flow in the other hot wire must be simultaneously
interrupted. This is hard to do with fuses (i.e. if your panel
uses fuses and you are working on a 240V circuit, make sure to
remove both fuses before thinking the circuit is deenergized).

A single device is supposed to only draw 12 amps (80% of 15) from
an outlet on a 15 amp circuit. Or a single device is supposed to
only draw 16 amps (80% of 20) from an outlet on a 20 amp circuit.

If you have an appropriate outlet, e.g. 120V 20A twist lock, and
no other loads (that are in use) then it may be safe for one
device to draw 20 amps from a 20 amp circuit. You just have to
keep in mind why the limits are there (to prevent overheating),
understand the actual performance of a 20 amp circuit breaker
(i.e. it doesn't instantly trip right at 20.001 amps), and know
how much safety margin is built into the NEC's ampacity tables.

> However, I'm wondering why the power outlet is limited to 15A?
> Is it because of the wiring?

Because of the size of the circuit interrupter which was based on
the size of the wire installed in the walls. In residences, it is
usually 15 amps or 20 amps for 120V circuits. 240V circuits are
usually 30 amps or 40 amps, sometimes 50 amps (jacuzzi tubs and
air conditioners).

> If there are multiple outlets in the garage, and each is rated to
> 15A, then I should be able to find the "first" outlet in the garage
> (where the supply wires come into the garage) and wire up a beefier
> outlet at that point. The wiring up to that point should be able
> to handle more current -- theoretically 15A x Num_Outlets. Is this
> correct?

No. A 15 amp circuit uses wire from the panel to all outlets in that
chain than can carry a maximum of 15 amps. So all N outlets have to
share the 15 amps.

> I'd also need to change the breaker for this circuit.

Breaker size _must_ be based on the ampacity of the smallest wire
used on that circuit. Otherwise, an overcurrent condition through
an outlet wired to the smaller gauge could cause overheating inside
the wall and a fire.

> I don't mind getting an electrician in there to add an outlet and
> run some lines from the breaker panel, etc, but I can't get them
> to run larger lines into the garage without raising some eyebrows.

The raised eyebrows will come when you get the electrician in to do
the work (assuming you are renting, the landlord will want to know
why you need a tenant improvement). Size of the wires pulled in by
the electrician is difficult to determine except through close
inspection, i.e. it's not obvious.

> > But just to make things complicated they fit the same plug. (there
> > are differences between 15 and 20 amp rated sockets, but the consumer
> > can't tell the difference by looking). It's still safe though, because
> > a 15 amp socket is protected by a 15 amp breaker. But it can certainly
> > be annoying.
>
> It's easy to tell the difference. If a device draws 15 amps or less,
> the standard plug has 1 round ground prong and 2 vertical blades for
> hot & neutral. If a device will draw between 15 and 20 amps, then the
> hot blade is horizontal (neutral blade is vertical & ground is round).

Yes, those do exist, but I've never seen them installed in a residential setting, nor have I seen any consumer equipment that has that plug fitted.

>
>Neutral line from pole is hooked up to ground distribution bus bar
>inside breaker panel. House is supposed to have a good quality earth
>ground with high ampacity wire connecting it to panel's ground bus.
>So neutral line from pole should be grounded at both ends (i.e. on
>the pole and inside the house's breaker panel).
>

> Please help with the terminology... what is a 'shower' in this context?
given that we are talking about high power electrical appliances he clearly
means an electrically powered instant heat shower. in the uk these tend to
range from 7-10KW.

I'm also am compelled to say I work with a few people who clearly don't know what they are either...

Mike

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>Please help with the terminology... what is a 'shower' in this context?

a shower over a bath, or in its own cubicle.

In the UK it is common to have an electrically heated shower unit that
heats the water as it flows, instead of drawing water from the household
hot water cylinder. Such a unit will be wired on its own circuit as they
do draw a reasonable amount of current.

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not make any use of this information, or copy or show it to any
person. Please contact us immediately to tell us that you have
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At 09:58 AM 10/19/2006, Aaron wrote:
> >
> >Neutral line from pole is hooked up to ground distribution bus bar
> >inside breaker panel. House is supposed to have a good quality earth
> >ground with high ampacity wire connecting it to panel's ground bus.
> >So neutral line from pole should be grounded at both ends (i.e. on
> >the pole and inside the house's breaker panel).

Not really - the ground conductivity is usually several orders of
magnitude less than resistance of the neutral conductor.

The terminology might be what's messing you up. The pole transformer
(residential) has an isolated secondary winding: 240 Vac
center-tapped. All 3 wires go into the house. In addition, the
center-tap (neutral) is grounded to earth with a ground rod at the
pole *and* another ground rod (or 2) at the house.

>
> >
> >Neutral line from pole is hooked up to ground distribution bus bar
> >inside breaker panel. House is supposed to have a good quality earth
> >ground with high ampacity wire connecting it to panel's ground bus.
> >So neutral line from pole should be grounded at both ends (i.e. on
> >the pole and inside the house's breaker panel).
> >
>
> Doesn't this create a ground loop?

If only it were that simple. I've done electrical work in two neighboring
counties, they used different building codes {CABO vs BOCA, IIRC} One
_required_ that the ground and neutral lines be connected at the service
panel, the other _prohibited_ them from being connected. And when questioned
both inspectors claimed the other way was unsafe.

> If only it were that simple. I've done electrical work in two
> neighboring
> counties, they used different building codes {CABO vs BOCA, IIRC} One
> _required_ that the ground and neutral lines be connected at
> the service
> panel, the other _prohibited_ them from being connected. And
> when questioned
> both inspectors claimed the other way was unsafe.

> If only it were that simple. I've done electrical work in two neighboring
> counties, they used different building codes {CABO vs BOCA, IIRC} One
> _required_ that the ground and neutral lines be connected at the service
> panel, the other _prohibited_ them from being connected. And when
> questioned both inspectors claimed the other way was unsafe.

I think the unsafe part when connected is that the ground wire may pick up
a potential if there is considerable current through the neutral wire to
ground. The unsafe part when not connected is probably that the ground wire
may be on a different potential than the neutral wire.

But I don't really see what should be unsafe when not connected (assuming
that the ground wire is properly grounded). I guess if I were asked to
design the wiring, I'd ground the ground wire separately. IMO that's the
purpose of a ground wire.

At 12:30 PM 10/19/2006, Gerhard Fiedler wrote:
>Denny Esterline wrote:
>
>But I don't really see what should be unsafe when not connected (assuming
>that the ground wire is properly grounded). I guess if I were asked to
>design the wiring, I'd ground the ground wire separately. IMO that's the
>purpose of a ground wire.

Think of what happens if the ground wire at the pole becomes
disconnected and where was no earth - neutral tie at the panel. In
that case, the entire circuit is free to float.

Two problems with a floating circuit: DC drift (triboelectric charge
due to wind on overhead service drops) and AC capacitively coupled
from the primary of the pole transformer.

Ensuring that the neutral is grounded both at the pole and at the
premises reduces the chance of the above happening.

>>> But just to make things complicated they fit the same plug. (there
>>> are differences between 15 and 20 amp rated sockets, but the consumer
>>> can't tell the difference by looking). It's still safe though, because
>>> a 15 amp socket is protected by a 15 amp breaker. But it can certainly
>>> be annoying.

>> It's easy to tell the difference. If a device draws 15 amps or less,
>> the standard plug has 1 round ground prong and 2 vertical blades for
>> hot & neutral. If a device will draw between 15 and 20 amps, then the
>> hot blade is horizontal (neutral blade is vertical & ground is round).

> Yes, those do exist, but I've never seen them installed in a residential
> setting, nor have I seen any consumer equipment that has that plug fitted.

Well, I have a couple in my garage (I installed them).

Oddly, I've also seen them fairly commonly in the hallways of light
commercial (i.e. office) buildings. I suspect it may be for the
floor polisher equipment since the vacuum cleaners don't need them.

> Oddly, I've also seen them fairly commonly in the hallways of light
> commercial (i.e. office) buildings. I suspect it may be for the
> floor polisher equipment since the vacuum cleaners don't need them.
also i've heared some installers like to install T slot recepticles as a
visual indication that a circuit is a 20A one even if it is unlikely that
any one appliance will need that much power.

>> But I don't really see what should be unsafe when not connected
>> (assuming that the ground wire is properly grounded). I guess if I were
>> asked to design the wiring, I'd ground the ground wire separately. IMO
>> that's the purpose of a ground wire.
>
> Think of what happens if the ground wire at the pole becomes
> disconnected and where was no earth - neutral tie at the panel. In
> that case, the entire circuit is free to float.

I guess I wasn't clear. I see the point of having the neutral grounded at
the panel (and was assuming it continues to be grounded). But I still think
that having the ground wire grounded separately and not connected to the
neutral would be safer.

On 10/19/06, Gerhard Fiedler <TakeThisOuTlistsEraseMEspam_OUTconnectionbrazil.com> wrote:
> Dwayne Reid wrote:
>
> >> But I don't really see what should be unsafe when not connected
> >> (assuming that the ground wire is properly grounded). I guess if I were
> >> asked to design the wiring, I'd ground the ground wire separately. IMO
> >> that's the purpose of a ground wire.
> >
> > Think of what happens if the ground wire at the pole becomes
> > disconnected and where was no earth - neutral tie at the panel. In
> > that case, the entire circuit is free to float.
>
> I guess I wasn't clear. I see the point of having the neutral grounded at
> the panel (and was assuming it continues to be grounded). But I still think
> that having the ground wire grounded separately and not connected to the
> neutral would be safer.

It's about what happens if the hot wire shorts to a grounded part of
an appliance. If such a short exists, you need continuity from the
ground wire to the neutral at the transformer in order to trip the
breaker. If the ground wire is grounded separately, you rely on the
quality of the ground connections and that of the earth between them.
Tie the ground to the neutral and you can be pretty sure that with
such a short, the breaker will trip.

A problem with the ground tied to the neutral is if the neutral back
to the transformer is broken. All sorts of strange things start
happening depending on how well the two phases (talking 180 deg
phases) are balanced and how good the earth grounds are... lights that
are dim but get brighter if you run something on the other phase and
so on. Not to mention unfriendly voltages on grounded parts.

>> I guess I wasn't clear. I see the point of having the neutral grounded
>> at the panel (and was assuming it continues to be grounded). But I
>> still think that having the ground wire grounded separately and not
>> connected to the neutral would be safer.
>
> It's about what happens if the hot wire shorts to a grounded part of
> an appliance. If such a short exists, you need continuity from the
> ground wire to the neutral at the transformer in order to trip the
> breaker.

That's why there should be a GFCI. Then the ground current is enough to
break the interrupter, without having to have the ground connected to
neutral.

On 10/19/06, Gerhard Fiedler <RemoveMElistsTakeThisOuTconnectionbrazil.com> wrote:
> Orin Eman wrote:
>
> >> I guess I wasn't clear. I see the point of having the neutral grounded
> >> at the panel (and was assuming it continues to be grounded). But I
> >> still think that having the ground wire grounded separately and not
> >> connected to the neutral would be safer.
> >
> > It's about what happens if the hot wire shorts to a grounded part of
> > an appliance. If such a short exists, you need continuity from the
> > ground wire to the neutral at the transformer in order to trip the
> > breaker.
>
> That's why there should be a GFCI. Then the ground current is enough to
> break the interrupter, without having to have the ground connected to
> neutral.

>>>cookers and showers are the only *common* domestic hard wired
>>>appliances here.
>>>
>>>
>>Please help with the terminology... what is a 'shower' in this context?
>>
>>
>
>
>A shower is a water sprinkler which you stand under to wash.
>
>

Yeah, we do that too.

The idea of one requiring electricity was foreign to me, but it seems as
if in the UK it is common for the shower to have it's own integrated
water heater. Are they all that way over there?

>>Please help with the terminology... what is a 'shower' in this context?
>>
>>
>given that we are talking about high power electrical appliances he clearly
>means an electrically powered instant heat shower. in the uk these tend to
>range from 7-10KW.
>
>
Thanks for the clarification. Where I live (USA), hot water for our
showers is supplied directly from the household hot water heater. This
is normally a 40ish gallon tank that supplies hot water to every
appliance/fixture in the house that requires it.. I know of a few
people with "on-demand" water heaters for remote fixtures, but none
dedicated specifically to the shower.

>
> The idea of one requiring electricity was foreign to me, but it seems as
> if in the UK it is common for the shower to have it's own integrated
> water heater. Are they all that way over there?
no, mixer showers are also pretty common, instant heat showers have the big
advantage though that when your boiler breaks or your hot water tank empties
you can still have a nice hot shower.

On 20/10/06, Aaron <aaron.piclistEraseME.....gmail.com> wrote:
> The idea of one requiring electricity was foreign to me, but it seems as
> if in the UK it is common for the shower to have it's own integrated
> water heater. Are they all that way over there?
>

No, not at all. Most people have stored hot water. But, the majority
of the stored hot water installations have a hot water cylinder which
is fed with cold water from a cold storage tank in the loft. Thus, the
hot pressure is low - only maybe 6ft of head at the shower.

Therefore, a lot of people choose one of the instantaneous heating
showers, these are fed with mains pressure cold water and thus give a
more powerful shower.

Some people have showers that are pumped to compensate for the low
pressure (like me), some people have unvented hot water cylinders -
where the hot water is at, or close to, mains pressure. These have
only relatively recently been legalised in the UK (in the last 10
years) so aren't ubiquitous yet. (The can be dangerous - a lot of hot
water under pressure can be a bit like a bomb if installed wrongly or
if a fault occurs (and the safety devices fail) - and also there are
tight regulations about preventing backflow of "contaminated" water
into the mains).

Increasingly common are central heating / hot water installations
powered by a "combi" boiler - this uses natural gas to instantaneously
heat the hot water, negating the need for storage, and provided mains
pressure hot water for a good shower. But you need a pretty powerful
combi to give a good flow rate at the shower (ie. 30KW +)

> Some people have showers that are pumped to compensate for the low
> pressure (like me), some people have unvented hot water cylinders -
> where the hot water is at, or close to, mains pressure. These have
> only relatively recently been legalised in the UK (in the last 10
> years) so aren't ubiquitous yet.

Huh. AFAIK, this is the only type of (tank) hot water heater used in
the
US. Whole-house instant heaters are gaining popularity in the US for
energy-efficiency reasons, but my impression is that the sort of
per-bathroom (or per-shower) heater you talk about is very uncommon.

Perhaps it has something to do with only having 110V, or the commonality
of central gas for heating rather than electricity.

>The idea of one requiring electricity was foreign to me, but it seems
as
>if in the UK it is common for the shower to have it's own integrated
>water heater. Are they all that way over there?

With the number of very old houses in the UK, which people attempt to
update to reasonably modern fittings, these devices are a popular way of
providing a local hot water source rather than attempting to run an
extra water pipe (which may fall foul of Historic Places building
requirements, if the property has listed status) which can involve a lot
of work.

Also used a lot where an ordinary house has set up as a bed and
breakfast place, and the original domestic water heating will not be up
to the task of supplying multiple on-suite units with hot water. They
make for an easy add-on to the existing system.

> > if in the UK it is common for the shower to have it's own
> > integrated water heater. Are they all that way over there?
>
> With the number of very old houses in the UK, which people
> attempt to update to reasonably modern fittings, these devices
> are a popular way of providing a local hot water source

Are these like Zip heaters ? We had a gas one, separate from
the electric hot water system, you'd to fire up to have a bath. I've
seen them in the kitchen and laundry too. Heaven help you if you
didn't make sure the thing had water in it (had a glass tube up the
outside)

...and sometimes those integrated devices gives a better feeling as in the
UK (and in Ireland) the hot water is not under pressure and needs some water
pumps to deliver the water which is of course generates a different pressure
than the supplier pipes have. The whole thing is weird because the cold and
hot mixture depends on the shower head's actual position, so it is too hot
when you place it on your knees but too cold when would like to wash your
head. Only the latest systems are good enough to work around this problem
while in the continent it is an evidence that the hot water is always under
pressure no matter if it is a gas powered flow-though boiler or an
electrical heated tank.

>
> >The idea of one requiring electricity was foreign to me, but it seems
> as
> >if in the UK it is common for the shower to have it's own integrated
> >water heater. Are they all that way over there?
>
> With the number of very old houses in the UK, which people attempt to
> update to reasonably modern fittings, these devices are a popular way of
> providing a local hot water source rather than attempting to run an
> extra water pipe (which may fall foul of Historic Places building
> requirements, if the property has listed status) which can involve a lot
> of work.
>
> Also used a lot where an ordinary house has set up as a bed and
> breakfast place, and the original domestic water heating will not be up
> to the task of supplying multiple on-suite units with hot water. They
> make for an easy add-on to the existing system.
>

>Are these like Zip heaters ? We had a gas one, separate from the
electric
>hot water system, you'd to fire up to have a bath. I've seen them in
the
>kitchen and laundry too. Heaven help you if you didn't make sure the
thing
>had water in it (had a glass tube up the outside)

No, a Zip is a storage tank (hence the tube to see the level). The
electric ones we're talking about heat the water as it flows, and has no
storage of hot water. Typically there are one or two knobs on the front,
to turn the water flow on and to adjust the temperature.

On 20/10/06, William Chops Westfield <RemoveMEwestfwEraseMEEraseMEmac.com> wrote:
> Perhaps it has something to do with only having 110V, or the commonality
> of central gas for heating rather than electricity.
>
> BillW

The majority of houses in the UK have mains gas supply. These kind of
showers are common in houses that have gas, as well as
electricity-only dwellings.

> Increasingly common are central heating / hot water installations
> powered by a "combi" boiler - this uses natural gas to instantaneously
> heat the hot water, negating the need for storage, and provided mains
> pressure hot water for a good shower. But you need a pretty powerful
> combi to give a good flow rate at the shower (ie. 30KW +)

i can't see why it would need to be as much as 30KW for a decent shower
given that electric showers are only about 10.

> Over here everything is three-phase: generation, transmission
> and distribution, until it gets to the individual property.
> At the local end of things there is a "substation" which has
> a 3-phase Wye-wound transformer that brings it down from 11kV
> to (nominally) 400V 3-phase, and a 3-phase cable runs from
> here down the street and each house in turn is fed one phase
> which gives a nominal 230V (I have a blue label with "B" on
> my distrubution board, so I'm on the Blue phase).

So it's a really bad idea to run an extension cord over to a friends house
to "steal" power if yours is not on yet?

Also makes one wonder about running network cables or phone lines over the
fence. Well... I guess all those things are supposed to be isolated anyway.

In any case, it's interesting to know that from one house to the next, the
AC appliances are most likely 120' out of phase with each other. Probably
not something that would ever make any difference, but...

> So it's a really bad idea to run an extension cord over to a friends house
> to "steal" power if yours is not on yet?
well there may well be 415V between thier live and your live yes, that
shouldn't pose a danger if all the equipment is in good condition and up to
standards though. A greater risk is the two properties may have different
earthing arrangements.

> Also makes one wonder about running network cables or phone lines over the
> fence. Well... I guess all those things are supposed to be
> isolated anyway.
as before ground potential differences are more of an issue than different
phases, both ethernet and phone are isolated interfaces for a reason though
;)

> In any case, it's interesting to know that from one house to the next, the
> AC appliances are most likely 120' out of phase with each other. Probably
> not something that would ever make any difference, but...
the fun begins when a neutral in the supply system breaks, if the load is
reasonablly balanced then things keep working, but nonlinear loads like pcs
and switching surges will cause the broken side of the neutral to jump all
over the place, this is good at frying light bulbs and doesn't do sensitive
electronics much good either.

> > I read the history of British electrical systems once and as I recall, the loop system was implemented to save metal. Since any plug is actually fed
from both sides of the loop the wire only needs to be rated for ~1/2 the total current. Ours is a single ended daisy chain, so the wire must be rated
for the full current. But we only have a fuse/breaker at the service panel, so the sum current of the entire string can't exceed the rated current. In
practice handheld appliances seem to rated less than 1500W (hair dryers, electric fry pans, tea kettles etc)
> >
>
> It's true. We call it a "ring final" circuit.

Ah, so you're a professional sparky then! :-) You used the proper term, whereas everyone else calls it a "ring main"...

> It's other benefit is
> that the CPC (the ground) is connected from two places, so is half as
> likely to be broken.

It also reduces the effect of any high resistance, such as loosely-clamped wire in a socket, because of the sharing of the load in both directions. A
radial ("daisy-chain") circuit relies on every connection being a good one, and the importance of this increases as you approach the feed end.

> Every socket in the UK has an earth (ground) pin (at least every
> socket made since the '20s). Every plug has a fuse in it, although in
> some situations a faulty appliance may trip the circuit's breaker
> rather than blow the fuse (due to the fuse blow characteristics)

And if you have *really* gone for it, the service fuse too! :-)

> Your handheld appliances are all rated below 1500W because of the way
> your houses are wired. Over here, it's common for appliances to pull
> much more - because they can. Kettles are often 2-2.5KW,

Actually I was looking at a few in a shop recently, and nowadays most of them seem to be rated at 3kW (at 240V of course, since at 230V that would
be over 13A).

> we have
> electric heaters at 2KW, etc. Of course, yours still work - but ours
> boil the water / heat the house quicker.

Again, a three-bar electric fire would be 3Kw, and we had one when I was a kid (early 1960's), and I remember the fishy smell the plug would give
off it you ran all three bars all evening, as my father tended to do, especially in the Winter of '63...

> > > If you're doing something industrial that needs more than 3kW you can either hard-wire, or use industrial plugs which handle 16 or 32A, but
you'd
> > > never normally see those in a house or garage, even a garage-workshop.
> > >
>
> That's the same here. The maximum any one socket is designed to deliver is 13A.

> > Most commonly circuits are 14ga wire and rated for 15 amps. Some specific circuits are rated for 20 amps and use 12ga wire
>
> We measure cable here in square millimetres. But, according the IEE
> Wiring Regulations (the UK electrical code), a cable doesn't have a
> rating *per se*. Rather the designer of the installation must
> calculate a suitable size of cable based on it's expected load, length
> (for meeting voltage drop requirements), the way it's installed (ie,
> embedded in a wall, clipped to a wall) for thermal derating, and
> whether it's grouped with other cables, as well as the earth fault
> loop impedance (which must be low enough to ensure that the circuit
> breakers will break within the required time when a dead short
> occurs).

Right, but you must admit that *most* 32A ring finals are wired in 2.5mm² Twin & Earth. There are time where the calculations would mean you'd
have to go to 4mm², but that would be exceptional. (That's square millimetres, in case the little 2 doesn't travel!)

> > Hard wire is reasonably common for lots of things, but we also have a myriad of other plugs for high current devices to about 50A. Electric clothes
dryers at 220V 30A, electric ranges at 220V 50A. Higher than that is common enough in industrial settings (I've seen 480V 500A three phase
connectors)
>
> cookers and showers are the only *common* domestic hard wired appliances here.

And Immersion Heaters and the supply for gas boilers - for the latter not because of the current requirement, which is only a couple of amps, but
because it shouldn't be unplugged.

> > Another interesting quirk is the voltage. It's common to talk about 110/220, but some people say 120/240. The plug next to me actually measures
117V. Some other places I've lived were closer to 110V and I worked in one place that measured 124V. And even though the USA is "standardized" on
60 Hz, I believe there are a couple small islands up near Maine that use 50Hz and last I knew there was a generator plant at Niagara Falls that
produces 25Hz for a few industrial customers.
>
> Europe used to have a nominal 220V, and the UK used to have a nominal
> 240V. But these nominal voltages were defined with a tolerance.
>
> Recently, the nominal voltage in europe has been changed, to 230V.
> But, sneakily, the tolerances changed with it - in the UK it's 230V
> +6%/-10% . I believe (but not certain) that continental europe is 230V
> -6%/+10%.

Other way round, I think - I believe it's currently 230 +10/-6% in the UK, giving a top of the range of 253V, which where I am they occasionally exceed!
According to my UPS its maximum in the past 5 minutes was 249.6V, and that's not unusual, especially at this time of night. Now that's not a very
accurate meter, but it's not far out and it's certainly around 245V now.

> However, most houses still see about 240V at the wall. The tolerances
> neatly shift the burden of compatibility onto appliance manufacturers.

I believe they are going to widen it further, to 230V +/- 10% for the whole of Europe, giving a range of 207 to 253V.

> > As they say, The best thing about standards is there are so many to choose from.
> >
> I think that's one of the advantages of the fact that the UK is so
> small - we just have one standard.

Nowadays, yes, but within my lifetime there were still DC mains supplies in a few places in the UK!

As soon as everyone gets onto one standard, they come up with another one... when I was a lad the wires were red/black/green and the normal
thickness for ring finals was 7/.029 (seven strands of 29-thou wire), then it changed to red/black/green&yellow, 2.5mm² single strand, now the wire's
the same but the colours are brown/blue/green&yellow. Ah well, it all makes for an interesting life! :-)

(I know this is a late reply - I was born a fortnight late, and I've never managed to catch up... )

On Wed, 18 Oct 2006 23:56:17 -0400, Denny Esterline wrote:

> I read the history of British electrical systems once and as I recall, the loop system was implemented to save metal. Since any plug is actually fed
from both sides of the loop the wire only needs to be rated for ~1/2 the total current.

Yes, although there is quite a bit of headroom on the "half" - the most common ring final will have a 32A Miniature Circuit Breaker (MCB) and will be
wired in 2.5mm² Cross-Sectional Area (CSA) "Twin & Earth" cable, which looks like this: http://www.tlc-direct.co.uk/Images/Products/size_3/CA2.5GH.JPG As you can see, the Earth core is uninsulated, but it will be covered with a
green/yellow sleeve within the backboxes of any socket, switch, etc. It has a free air rating of 27A (if my memory serves), although this is reduced
in most real-world installations to 23A, as you can see there is plenty of headroom.

> Ours is a single ended daisy chain, so the wire must be rated for the full current. But we only have a fuse/breaker at the service panel, so the sum
current of the entire string can't exceed the rated current. In practice handheld appliances seem to rated less than 1500W (hair dryers, electric fry
pans, tea kettles etc)

We call this a "Radial" circuit, and they are used for lighting (which is always separate from power circuits), and for single-appliance circuits such as
electric cookers. They can be used for strings of sockets, but because you have to use thicker cable (typically 4mm²) it's unusual - a 2.5mm² ring is
much easier to work with.

> > If you're doing something industrial that needs more than 3kW you can either hard-wire, or use industrial plugs which handle 16 or 32A, but you'd
> > never normally see those in a house or garage, even a garage-workshop.
> >
>
> Most commonly circuits are 14ga wire and rated for 15 amps. Some specific circuits are rated for 20 amps and use 12ga wire (I believe it's 2 in the
kitchen by local code) and usually in the utility area (garage, basement, outdoor...)

We have no regulations here about how many circuits are provided, or where - my own house has two power rings, upstairs and down (32A each),
and had a single lighing circuit for the whole house, but I split this into two when I installed a new Consumer Unit (I think you call this a distribution
board?) back in 2004 when it was still allowed to do this without Building Control approval. Then there's a radial for the immersion heater and
another one for the fridge/freezer (16A each, the latter so that a trip caused by a fault elsewhere while I'm away won't mean all my food goes bad!).
Then there's the shed...

> But just to make things complicated they fit the same plug. (there are differences between 15 and 20 amp rated sockets, but the consumer can't
tell the difference by looking) It's still safe though, because a 15 amp socket is protected by a 15 amp breaker. But it can certainly be annoying.

I was a bit amazed at my girlfriend's house in New York to discover that a single 15A breaker powers the ground floor lights, all of the kitchen except
the fridge/freezer, the dining room and the living room sockets. I discovered this when I tried to use the microwave and the toaster at the same time,
and it all went dark and quiet! :-) At home if I use my microwave (1kW) and electic kettle (2.2kW) together it doesn't even come half way to the
downstairs ring's current rating - it would never occur to me to be careful how much I use at once!

Having read some of your NEC, it strikes me that it's focus is almost all on prevention of overheating and fire - over here prevention of electric shock
has at least the same emphasis, if not more. And it seems to rely on active safety devices like GFCIs (which we call RCDs), rather than the design
and installation being naturally safe - for example sockets aren't allowed in a bathroom (to the annoyance of my girlfriend because she can't use a
hairdryer in there :-) except special 1-Amp-fused 2-pin sockets supplied from an integral isolating transformer, for electric shavers and toothbrush
chargers, such as this one: http://www.tlc-direct.co.uk/Images/Products/size_3/MKK701.JPG. Interestingly it's dual-voltage, so visiting Americans can
charge their toothbrushes! :-) This is the only place you'll find 115V in a UK house.

>...
> Another interesting quirk is the voltage. It's common to talk about 110/220, but some people say 120/240. The plug next to me actually measures
117V. Some other places I've lived were closer to 110V and I worked in one place that measured 124V. And even though the USA is "standardized" on
60 Hz, I believe there are a couple small islands up near Maine that use 50Hz and last I knew there was a generator plant at Niagara Falls that
produces 25Hz for a few industrial customers.

124V on a nominal 110V sounds a bit out of spec! Is there a published allowable range?

Ours is all 50Hz, and as has been discussed it's *nominally* 230V, but mine is currently at 244V, which isn't unusual.